Towed seismic streamers containing a hydrophone array have been in use for some time as data gatherers. The information obtained has been of particular interest for oil exploration, and other marine geophysical studies, to name a few. Typical examples of the evolving state-of-the-art are shown in U.S. Pat. No. 2,465,696 to Leroy C. Paslay for his Method and Means of Surveying Geological Formations; the Pressure Cable Construction of F. G. Blake et al in U.S. Pat. No. 2,791,757; the Method and Underwater Streamer Apparatus for Improving the Fidelity of Recorded Seismic Signals of G. M. Pavey, Jr. et al in U.S. Pat. No. 3,290,645 as well as Pavey's later apparatus of U.S. Pat. No. 3,319,734; Frank R. Abbott's Towable Sonar Array With Depth Compensation of U.S. Pat. No. 3,868,623 and J. J. Babbs Shallow Water Seismic Prospecting Cable of U.S. Pat. No. 3,435,410. These patents show typical examples of the efforts undertaken to upgrade the validity of the data obtained by using improved transducers, data processing techniques and general design considerations. All these designs represent advances in the state-of-the-art; however, it is safe to say that all would seek to improve the validity of the collected data to one degree or another.
One aspect of design allowing the quality of the gathered data to be improved is the provision of a device for blocking mechanical shocks and vibrations originating in other structural members from reaching the array. The streamlined outer surface presented by a hose-like sheath in most of the patents cited above represents an attempt to avoid some of the motional disturbances to the acoustic sensors. Yet, high speed towing creates unwanted shock and vibration due to unsteady motion of the towing platform, vibration of the propulsion machinery, strumming of the tow cable, and unstable motion of the drogue used to tension the array. These many mechanical disturbances, if allowed to propagate to the acoustic sections of the array, cause accelerations and pressure fluctuations within the array that are monitored and converted into erroneous signals by the receiving transducers.
An attempt to reduce the motional disturbances has been the inclusion of vibration isolation modules. Currently, the modules typically consist of an outer plastic hose, a fill fluid, an internal compliant member or members (usually in the form of a nylon rope), an internal slack essentially nonextensional member or members (usually in the form of a steel cable or a rope made of very strong, stiff aramid fiber such as that marketed under the DuPont Company trademark KEVLAR), appropriate very slack electrical conductors, and suitable end caps. At very low speeds the load of the vibration isolation module and its towed array is carried by the hose wall alone. When somewhat higher speeds are reached, the load is carried by the hose wall and the internal compliant member jointly. Within these lower speed regimes the vibration isolation module functions primarily as a spring with some damping resulting from tensional losses in both the hose wall and the compliant member and from viscous flow in the fill fluid.
Traveling at some still higher speed the hose wall and compliant member "bottom out" when the essentially nonextensional member becomes taut. At this point all vibration and shock isolation is lost and the array is subject to accelerated wear and early failure.
Thus there is a continuing need in the state-of-the-art for a vibration isolation module that provides for greater damping and higher dynamic range without "bottoming out" or being permanently stretched, and which also more effectively reduces the influences of longitudinal shock and other longitudinal motional disturbances from compromising the response of the towed acoustic array. Such a device would also find applications where such shocks and disturbances were to be isolated from members attached to opposite ends of the modules such as in a restraint harness, between a towed barge and a tug or in an instrumentation package suspended from shipboard or a buoy.